CVE-2026-20221

Multiple Cisco products are affected by a vulnerability in the generic routing encapsulation (GRE) tunnel decapsulation feature of the Snort 3 Detection Engine that could allow an unauthenticated, remote attacker to cause an unexpected restart of the Snort 3 Detection Engine. This vulnerability is due to improper handling of nested GRE traffic. An attacker could exploit this vulnerability by sending a crafted GRE payload through an affected device. A successful exploit could allow the attacker to trigger an unexpected reload of the Snort 3 Detection Engine, resulting in either a bypass or denial of service (DoS) condition, depending on device configuration. For more information, see the section of this advisory. The Snort 3 Detection Engine will restart automatically. No manual intervention is required.

CVSS v3 5.8 MEDIUM

5.8^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact LOW

Scope CHANGED

References

Link	Resource
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort3-gre-JNpMHrTv

Configurations

No configuration.

History

21 Oct 2026, 17:18

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-21 17:18

Updated : 2026-10-22 14:17

NVD link : CVE-2026-20221

Mitre link : CVE-2026-20221

CVE.ORG link : CVE-2026-20221

JSON object : View

Products Affected

No product.

CWE

CWE-476

NULL Pointer Dereference

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"affected", "version": "17.12.5"}, {"status": "affected", "version": "17.17.1"}, {"status": "affected", "version": "17.12.5a"}, {"status": "affected", "version": "17.9.7a"}, {"status": "affected", "version": "17.15.3a"}, {"status": "affected", "version": "17.15.3"}, {"status": "affected", "version": "17.12.5b"}, {"status": "affected", "version": "17.12.5c"}, {"status": "affected", "version": "17.15.4"}, {"status": "affected", "version": "17.9.7b"}, {"status": "affected", "version": "17.18.1"}, {"status": "affected", "version": "17.18.1a"}, {"status": "affected", "version": "17.12.6"}, {"status": "affected", "version": "17.9.8"}, {"status": "affected", "version": "17.15.4c"}, {"status": "affected", "version": "17.12.5d"}, {"status": "affected", "version": "17.18.2"}, {"status": "affected", "version": "26.1.1"}, {"status": "affected", "version": "17.15.5"}, {"status": "affected", "version": "17.15.5a"}, {"status": "affected", "version": "17.12.7"}, {"status": "affected", "version": "17.12.7a"}, {"status": "affected", "version": "17.12.7b"}, {"status": "affected", "version": "17.9.9"}, {"status": "affected", "version": "17.18.3a"}, {"status": "affected", "version": "17.12.8"}, {"status": "affected", "version": "17.15.6"}, {"status": "affected", "version": "17.18.4"}, {"status": "affected", "version": "26.1.2"}, {"status": "affected", "version": "17.9.10"}], "defaultStatus": "unknown"}]}], "published": "2026-10-21T17:18:27.947", "references": [{"url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort3-gre-JNpMHrTv", "source": "psirt@cisco.com"}], "vulnStatus": "Awaiting Analysis", "weaknesses": [{"type": "Secondary", "source": "psirt@cisco.com", "description": [{"lang": "en", "value": "CWE-476"}]}], "descriptions": [{"lang": "en", "value": "Multiple Cisco products are affected by a vulnerability in the generic routing encapsulation (GRE) tunnel decapsulation feature of the Snort 3 Detection Engine that could allow an unauthenticated, remote attacker to cause an unexpected restart of the Snort 3 Detection Engine.\r\n\r\nThis vulnerability is due to improper handling of nested GRE traffic. An attacker could exploit this vulnerability by sending a crafted GRE payload through an affected device. A successful exploit could allow the attacker to trigger an unexpected reload of the Snort 3 Detection Engine, resulting in either a bypass or denial of service (DoS) condition, depending on device configuration. For more information, see the section of this advisory. The Snort 3 Detection Engine will restart automatically. No manual intervention is required."}], "lastModified": "2026-10-22T14:17:40.940", "sourceIdentifier": "psirt@cisco.com"}